Material with morph support

I have a problem with the mesh of my character, when the character moves hes leg, there is a MORPH TARGET to fix deformations. The problem is when this morph target gets active, a weird shadow appears:


I readed in a forum that I needed to TURN ON USE WITH MORPH TARGETS in the USAGE panel when creating a new material, but the problem is still apearing


I tried re-importing with new smooth groups and nothing works
Someone knows how to fix this bug?